The invention relates to a procedure for the determination of the consumption of electrical energy by a consumer by the measurement of the sinusoidal alternating voltage applied to the consumer and the sinusoidal alternating current flowing to the consumer at points in time according to a pre-determined sampling rate, the formation of the product of the values measured, and the formation of the sum of the products for the duration of the energy consumption by the consumer.
For the determination of the energy consumption by a consumer, it is necessary, in principle, to obtain the product of the voltage applied to the consumer and of the current flowing through the consumer, and this product has to be integrated over the period of time when energy is consumed. At present it is standard practice to digitize the measured values thus obtained and to process these further in the form of digital data. The German patent specification No. 42 21 057 describes a procedure whereby the sine-shaped alternating voltage and the sine-shaped alternating current are sampled at periodic intervals, the values sampled are converted into digital values, and further processing in order to obtain the required energy value then proceeds on the basis of the digitized samples. To reduce the number of sampling processes required, the alternating voltage and the alternating current are alternately sampled at time intervals determined by the sampling rate, and the product is formed by using the present sample as well as the sample obtained from the previous sampling period. This procedure necessitates the application of a correction factor for the determination of the energy consumption, which is dependent on the frequency of both the alternating current and the alternating voltage, as well as on the sampling period. Because of this dependency, the application flexibility of this known procedure is limited, except in certain application cases where a measurement error can be tolerated.
The invention rests on the requirement to provide a procedure of the type previously indicated whereby, in spite of the time-shifted sampling of the voltage and current values, energy consumption values can be obtained, the precision of which is independent of the sampling period at which sampling of the voltage and current values takes place.
According to the invention, this requirement is met in that for each voltage value measured at a voltage-measurement point in time, in accordance with the timing interval of the sampling period, a current value is sampled, at points xcex94t before the voltage measurement point in time and xcex94t after the voltage measurement point in time, that the product is formed by multiplying each measured voltage value by the current value measured xcex94t before the voltage measurement point in time, and by the current value measured xcex94t after the voltage measurement point in time, and that for the formation of the sum, the arithmetic mean values of the products from each of the measured voltage values over the duration of consumption of energy by the consumer are added together.
When applying the procedure according to the invention, several products are formed at time intervals corresponding to the sampling period, that is from the sampled voltage value and the sampled current values immediately before and immediately after the point in time of the measurement. The mean values of the products formed from each sampled voltage value are added up for the duration of the energy consumption period. Although the energy consumption value obtained by the application of the procedure according to the invention contains a system-inherent measurement error, this depends only on the separation in time between the sampling points of the measured voltage value and those of the corresponding measured current values, whereby this time difference for the performance of the sampling process can be kept extremely short by using modern processors.
An advantageous further embodiment consists in that, in addition to the current values measured at xcex94t before and after the voltage measurement point, two further current values displaced by 2 xcex94t before and after the voltage measurement point are sampled, and that for the voltage value measured, products are formed of all four current values related to the voltage value concerned.
On the strength of this further embodiment, this system-implied error can be further reduced.